1============================================================================
23can.txt
45Readme file for the Controller Area Network Protocol Family (aka SocketCAN)
67This file contains
89 1 Overview / What is SocketCAN
1011 2 Motivation / Why using the socket API
1213 3 SocketCAN concept
14 3.1 receive lists
15 3.2 local loopback of sent frames
16 3.3 network problem notifications
1718 4 How to use SocketCAN
19 4.1 RAW protocol sockets with can_filters (SOCK_RAW)
20 4.1.1 RAW socket option CAN_RAW_FILTER
21 4.1.2 RAW socket option CAN_RAW_ERR_FILTER
22 4.1.3 RAW socket option CAN_RAW_LOOPBACK
23 4.1.4 RAW socket option CAN_RAW_RECV_OWN_MSGS
24 4.1.5 RAW socket option CAN_RAW_FD_FRAMES
25 4.1.6 RAW socket option CAN_RAW_JOIN_FILTERS
26 4.1.7 RAW socket returned message flags
27 4.2 Broadcast Manager protocol sockets (SOCK_DGRAM)
28 4.2.1 Broadcast Manager operations
29 4.2.2 Broadcast Manager message flags
30 4.2.3 Broadcast Manager transmission timers
31 4.2.4 Broadcast Manager message sequence transmission
32 4.2.5 Broadcast Manager receive filter timers
33 4.2.6 Broadcast Manager multiplex message receive filter
34 4.3 connected transport protocols (SOCK_SEQPACKET)
35 4.4 unconnected transport protocols (SOCK_DGRAM)
3637 5 SocketCAN core module
38 5.1 can.ko module params
39 5.2 procfs content
40 5.3 writing own CAN protocol modules
4142 6 CAN network drivers
43 6.1 general settings
44 6.2 local loopback of sent frames
45 6.3 CAN controller hardware filters
46 6.4 The virtual CAN driver (vcan)
47 6.5 The CAN network device driver interface
48 6.5.1 Netlink interface to set/get devices properties
49 6.5.2 Setting the CAN bit-timing
50 6.5.3 Starting and stopping the CAN network device
51 6.6 CAN FD (flexible data rate) driver support
52 6.7 supported CAN hardware
5354 7 SocketCAN resources
5556 8 Credits
5758============================================================================
59601. Overview / What is SocketCAN
61--------------------------------
6263The socketcan package is an implementation of CAN protocols
64(Controller Area Network) for Linux. CAN is a networking technology
65which has widespread use in automation, embedded devices, and
66automotive fields. While there have been other CAN implementations
67for Linux based on character devices, SocketCAN uses the Berkeley
68socket API, the Linux network stack and implements the CAN device
69drivers as network interfaces. The CAN socket API has been designed
70as similar as possible to the TCP/IP protocols to allow programmers,
71familiar with network programming, to easily learn how to use CAN
72sockets.
73742. Motivation / Why using the socket API
75----------------------------------------
7677There have been CAN implementations for Linux before SocketCAN so the
78question arises, why we have started another project. Most existing
79implementations come as a device driver for some CAN hardware, they
80are based on character devices and provide comparatively little
81functionality. Usually, there is only a hardware-specific device
82driver which provides a character device interface to send and
83receive raw CAN frames, directly to/from the controller hardware.
84Queueing of frames and higher-level transport protocols like ISO-TP
85have to be implemented in user space applications. Also, most
86character-device implementations support only one single process to
87open the device at a time, similar to a serial interface. Exchanging
88the CAN controller requires employment of another device driver and
89often the need for adaption of large parts of the application to the
90new driver's API.
9192SocketCAN was designed to overcome all of these limitations. A new
93protocol family has been implemented which provides a socket interface
94to user space applications and which builds upon the Linux network
95layer, enabling use all of the provided queueing functionality. A device
96driver for CAN controller hardware registers itself with the Linux
97network layer as a network device, so that CAN frames from the
98controller can be passed up to the network layer and on to the CAN
99protocol family module and also vice-versa. Also, the protocol family
100module provides an API for transport protocol modules to register, so
101that any number of transport protocols can be loaded or unloaded
102dynamically. In fact, the can core module alone does not provide any
103protocol and cannot be used without loading at least one additional
104protocol module. Multiple sockets can be opened at the same time,
105on different or the same protocol module and they can listen/send
106frames on different or the same CAN IDs. Several sockets listening on
107the same interface for frames with the same CAN ID are all passed the
108same received matching CAN frames. An application wishing to
109communicate using a specific transport protocol, e.g. ISO-TP, just
110selects that protocol when opening the socket, and then can read and
111write application data byte streams, without having to deal with
112CAN-IDs, frames, etc.
113114Similar functionality visible from user-space could be provided by a
115character device, too, but this would lead to a technically inelegant
116solution for a couple of reasons:
117118* Intricate usage. Instead of passing a protocol argument to
119 socket(2) and using bind(2) to select a CAN interface and CAN ID, an
120 application would have to do all these operations using ioctl(2)s.
121122* Code duplication. A character device cannot make use of the Linux
123 network queueing code, so all that code would have to be duplicated
124 for CAN networking.
125126* Abstraction. In most existing character-device implementations, the
127 hardware-specific device driver for a CAN controller directly
128 provides the character device for the application to work with.
129 This is at least very unusual in Unix systems for both, char and
130 block devices. For example you don't have a character device for a
131 certain UART of a serial interface, a certain sound chip in your
132 computer, a SCSI or IDE controller providing access to your hard
133 disk or tape streamer device. Instead, you have abstraction layers
134 which provide a unified character or block device interface to the
135 application on the one hand, and a interface for hardware-specific
136 device drivers on the other hand. These abstractions are provided
137 by subsystems like the tty layer, the audio subsystem or the SCSI
138 and IDE subsystems for the devices mentioned above.
139140 The easiest way to implement a CAN device driver is as a character
141 device without such a (complete) abstraction layer, as is done by most
142 existing drivers. The right way, however, would be to add such a
143 layer with all the functionality like registering for certain CAN
144 IDs, supporting several open file descriptors and (de)multiplexing
145 CAN frames between them, (sophisticated) queueing of CAN frames, and
146 providing an API for device drivers to register with. However, then
147 it would be no more difficult, or may be even easier, to use the
148 networking framework provided by the Linux kernel, and this is what
149 SocketCAN does.
150151 The use of the networking framework of the Linux kernel is just the
152 natural and most appropriate way to implement CAN for Linux.
1531543. SocketCAN concept
155---------------------
156157 As described in chapter 2 it is the main goal of SocketCAN to
158 provide a socket interface to user space applications which builds
159 upon the Linux network layer. In contrast to the commonly known
160 TCP/IP and ethernet networking, the CAN bus is a broadcast-only(!)
161 medium that has no MAC-layer addressing like ethernet. The CAN-identifier
162 (can_id) is used for arbitration on the CAN-bus. Therefore the CAN-IDs
163 have to be chosen uniquely on the bus. When designing a CAN-ECU
164 network the CAN-IDs are mapped to be sent by a specific ECU.
165 For this reason a CAN-ID can be treated best as a kind of source address.
166167 3.1 receive lists
168169 The network transparent access of multiple applications leads to the
170 problem that different applications may be interested in the same
171 CAN-IDs from the same CAN network interface. The SocketCAN core
172 module - which implements the protocol family CAN - provides several
173 high efficient receive lists for this reason. If e.g. a user space
174 application opens a CAN RAW socket, the raw protocol module itself
175 requests the (range of) CAN-IDs from the SocketCAN core that are
176 requested by the user. The subscription and unsubscription of
177 CAN-IDs can be done for specific CAN interfaces or for all(!) known
178 CAN interfaces with the can_rx_(un)register() functions provided to
179 CAN protocol modules by the SocketCAN core (see chapter 5).
180 To optimize the CPU usage at runtime the receive lists are split up
181 into several specific lists per device that match the requested
182 filter complexity for a given use-case.
183184 3.2 local loopback of sent frames
185186 As known from other networking concepts the data exchanging
187 applications may run on the same or different nodes without any
188 change (except for the according addressing information):
189190 ___ ___ ___ _______ ___
191 | _ | | _ | | _ | | _ _ | | _ |
192 ||A|| ||B|| ||C|| ||A| |B|| ||C||
193 |___| |___| |___| |_______| |___|
194 | | | | |
195 -----------------(1)- CAN bus -(2)---------------
196197 To ensure that application A receives the same information in the
198 example (2) as it would receive in example (1) there is need for
199 some kind of local loopback of the sent CAN frames on the appropriate
200 node.
201202 The Linux network devices (by default) just can handle the
203 transmission and reception of media dependent frames. Due to the
204 arbitration on the CAN bus the transmission of a low prio CAN-ID
205 may be delayed by the reception of a high prio CAN frame. To
206 reflect the correct* traffic on the node the loopback of the sent
207 data has to be performed right after a successful transmission. If
208 the CAN network interface is not capable of performing the loopback for
209 some reason the SocketCAN core can do this task as a fallback solution.
210 See chapter 6.2 for details (recommended).
211212 The loopback functionality is enabled by default to reflect standard
213 networking behaviour for CAN applications. Due to some requests from
214 the RT-SocketCAN group the loopback optionally may be disabled for each
215 separate socket. See sockopts from the CAN RAW sockets in chapter 4.1.
216217 * = you really like to have this when you're running analyser tools
218 like 'candump' or 'cansniffer' on the (same) node.
219220 3.3 network problem notifications
221222 The use of the CAN bus may lead to several problems on the physical
223 and media access control layer. Detecting and logging of these lower
224 layer problems is a vital requirement for CAN users to identify
225 hardware issues on the physical transceiver layer as well as
226 arbitration problems and error frames caused by the different
227 ECUs. The occurrence of detected errors are important for diagnosis
228 and have to be logged together with the exact timestamp. For this
229 reason the CAN interface driver can generate so called Error Message
230 Frames that can optionally be passed to the user application in the
231 same way as other CAN frames. Whenever an error on the physical layer
232 or the MAC layer is detected (e.g. by the CAN controller) the driver
233 creates an appropriate error message frame. Error messages frames can
234 be requested by the user application using the common CAN filter
235 mechanisms. Inside this filter definition the (interested) type of
236 errors may be selected. The reception of error messages is disabled
237 by default. The format of the CAN error message frame is briefly
238 described in the Linux header file "include/uapi/linux/can/error.h".
2392404. How to use SocketCAN
241------------------------
242243 Like TCP/IP, you first need to open a socket for communicating over a
244 CAN network. Since SocketCAN implements a new protocol family, you
245 need to pass PF_CAN as the first argument to the socket(2) system
246 call. Currently, there are two CAN protocols to choose from, the raw
247 socket protocol and the broadcast manager (BCM). So to open a socket,
248 you would write
249250 s = socket(PF_CAN, SOCK_RAW, CAN_RAW);
251252 and
253254 s = socket(PF_CAN, SOCK_DGRAM, CAN_BCM);
255256 respectively. After the successful creation of the socket, you would
257 normally use the bind(2) system call to bind the socket to a CAN
258 interface (which is different from TCP/IP due to different addressing
259 - see chapter 3). After binding (CAN_RAW) or connecting (CAN_BCM)
260 the socket, you can read(2) and write(2) from/to the socket or use
261 send(2), sendto(2), sendmsg(2) and the recv* counterpart operations
262 on the socket as usual. There are also CAN specific socket options
263 described below.
264265 The basic CAN frame structure and the sockaddr structure are defined
266 in include/linux/can.h:
267268 struct can_frame {
269 canid_t can_id; /* 32 bit CAN_ID + EFF/RTR/ERR flags */
270 __u8 can_dlc; /* frame payload length in byte (0 .. 8) */
271 __u8 data[8] __attribute__((aligned(8)));
272 };
273274 The alignment of the (linear) payload data[] to a 64bit boundary
275 allows the user to define their own structs and unions to easily access
276 the CAN payload. There is no given byteorder on the CAN bus by
277 default. A read(2) system call on a CAN_RAW socket transfers a
278 struct can_frame to the user space.
279280 The sockaddr_can structure has an interface index like the
281 PF_PACKET socket, that also binds to a specific interface:
282283 struct sockaddr_can {
284 sa_family_t can_family;
285 int can_ifindex;
286 union {
287 /* transport protocol class address info (e.g. ISOTP) */
288 struct { canid_t rx_id, tx_id; } tp;
289290 /* reserved for future CAN protocols address information */
291 } can_addr;
292 };
293294 To determine the interface index an appropriate ioctl() has to
295 be used (example for CAN_RAW sockets without error checking):
296297 int s;
298 struct sockaddr_can addr;
299 struct ifreq ifr;
300301 s = socket(PF_CAN, SOCK_RAW, CAN_RAW);
302303 strcpy(ifr.ifr_name, "can0" );
304 ioctl(s, SIOCGIFINDEX, &ifr);
305306 addr.can_family = AF_CAN;
307 addr.can_ifindex = ifr.ifr_ifindex;
308309 bind(s, (struct sockaddr *)&addr, sizeof(addr));
310311 (..)
312313 To bind a socket to all(!) CAN interfaces the interface index must
314 be 0 (zero). In this case the socket receives CAN frames from every
315 enabled CAN interface. To determine the originating CAN interface
316 the system call recvfrom(2) may be used instead of read(2). To send
317 on a socket that is bound to 'any' interface sendto(2) is needed to
318 specify the outgoing interface.
319320 Reading CAN frames from a bound CAN_RAW socket (see above) consists
321 of reading a struct can_frame:
322323 struct can_frame frame;
324325 nbytes = read(s, &frame, sizeof(struct can_frame));
326327 if (nbytes < 0) {
328 perror("can raw socket read");
329 return 1;
330 }
331332 /* paranoid check ... */
333 if (nbytes < sizeof(struct can_frame)) {
334 fprintf(stderr, "read: incomplete CAN frame\n");
335 return 1;
336 }
337338 /* do something with the received CAN frame */
339340 Writing CAN frames can be done similarly, with the write(2) system call:
341342 nbytes = write(s, &frame, sizeof(struct can_frame));
343344 When the CAN interface is bound to 'any' existing CAN interface
345 (addr.can_ifindex = 0) it is recommended to use recvfrom(2) if the
346 information about the originating CAN interface is needed:
347348 struct sockaddr_can addr;
349 struct ifreq ifr;
350 socklen_t len = sizeof(addr);
351 struct can_frame frame;
352353 nbytes = recvfrom(s, &frame, sizeof(struct can_frame),
354 0, (struct sockaddr*)&addr, &len);
355356 /* get interface name of the received CAN frame */
357 ifr.ifr_ifindex = addr.can_ifindex;
358 ioctl(s, SIOCGIFNAME, &ifr);
359 printf("Received a CAN frame from interface %s", ifr.ifr_name);
360361 To write CAN frames on sockets bound to 'any' CAN interface the
362 outgoing interface has to be defined certainly.
363364 strcpy(ifr.ifr_name, "can0");
365 ioctl(s, SIOCGIFINDEX, &ifr);
366 addr.can_ifindex = ifr.ifr_ifindex;
367 addr.can_family = AF_CAN;
368369 nbytes = sendto(s, &frame, sizeof(struct can_frame),
370 0, (struct sockaddr*)&addr, sizeof(addr));
371372 Remark about CAN FD (flexible data rate) support:
373374 Generally the handling of CAN FD is very similar to the formerly described
375 examples. The new CAN FD capable CAN controllers support two different
376 bitrates for the arbitration phase and the payload phase of the CAN FD frame
377 and up to 64 bytes of payload. This extended payload length breaks all the
378 kernel interfaces (ABI) which heavily rely on the CAN frame with fixed eight
379 bytes of payload (struct can_frame) like the CAN_RAW socket. Therefore e.g.
380 the CAN_RAW socket supports a new socket option CAN_RAW_FD_FRAMES that
381 switches the socket into a mode that allows the handling of CAN FD frames
382 and (legacy) CAN frames simultaneously (see section 4.1.5).
383384 The struct canfd_frame is defined in include/linux/can.h:
385386 struct canfd_frame {
387 canid_t can_id; /* 32 bit CAN_ID + EFF/RTR/ERR flags */
388 __u8 len; /* frame payload length in byte (0 .. 64) */
389 __u8 flags; /* additional flags for CAN FD */
390 __u8 __res0; /* reserved / padding */
391 __u8 __res1; /* reserved / padding */
392 __u8 data[64] __attribute__((aligned(8)));
393 };
394395 The struct canfd_frame and the existing struct can_frame have the can_id,
396 the payload length and the payload data at the same offset inside their
397 structures. This allows to handle the different structures very similar.
398 When the content of a struct can_frame is copied into a struct canfd_frame
399 all structure elements can be used as-is - only the data[] becomes extended.
400401 When introducing the struct canfd_frame it turned out that the data length
402 code (DLC) of the struct can_frame was used as a length information as the
403 length and the DLC has a 1:1 mapping in the range of 0 .. 8. To preserve
404 the easy handling of the length information the canfd_frame.len element
405 contains a plain length value from 0 .. 64. So both canfd_frame.len and
406 can_frame.can_dlc are equal and contain a length information and no DLC.
407 For details about the distinction of CAN and CAN FD capable devices and
408 the mapping to the bus-relevant data length code (DLC), see chapter 6.6.
409410 The length of the two CAN(FD) frame structures define the maximum transfer
411 unit (MTU) of the CAN(FD) network interface and skbuff data length. Two
412 definitions are specified for CAN specific MTUs in include/linux/can.h :
413414 #define CAN_MTU (sizeof(struct can_frame)) == 16 => 'legacy' CAN frame
415 #define CANFD_MTU (sizeof(struct canfd_frame)) == 72 => CAN FD frame
416417 4.1 RAW protocol sockets with can_filters (SOCK_RAW)
418419 Using CAN_RAW sockets is extensively comparable to the commonly
420 known access to CAN character devices. To meet the new possibilities
421 provided by the multi user SocketCAN approach, some reasonable
422 defaults are set at RAW socket binding time:
423424 - The filters are set to exactly one filter receiving everything
425 - The socket only receives valid data frames (=> no error message frames)
426 - The loopback of sent CAN frames is enabled (see chapter 3.2)
427 - The socket does not receive its own sent frames (in loopback mode)
428429 These default settings may be changed before or after binding the socket.
430 To use the referenced definitions of the socket options for CAN_RAW
431 sockets, include <linux/can/raw.h>.
432433 4.1.1 RAW socket option CAN_RAW_FILTER
434435 The reception of CAN frames using CAN_RAW sockets can be controlled
436 by defining 0 .. n filters with the CAN_RAW_FILTER socket option.
437438 The CAN filter structure is defined in include/linux/can.h:
439440 struct can_filter {
441 canid_t can_id;
442 canid_t can_mask;
443 };
444445 A filter matches, when
446447 <received_can_id> & mask == can_id & mask
448449 which is analogous to known CAN controllers hardware filter semantics.
450 The filter can be inverted in this semantic, when the CAN_INV_FILTER
451 bit is set in can_id element of the can_filter structure. In
452 contrast to CAN controller hardware filters the user may set 0 .. n
453 receive filters for each open socket separately:
454455 struct can_filter rfilter[2];
456457 rfilter[0].can_id = 0x123;
458 rfilter[0].can_mask = CAN_SFF_MASK;
459 rfilter[1].can_id = 0x200;
460 rfilter[1].can_mask = 0x700;
461462 setsockopt(s, SOL_CAN_RAW, CAN_RAW_FILTER, &rfilter, sizeof(rfilter));
463464 To disable the reception of CAN frames on the selected CAN_RAW socket:
465466 setsockopt(s, SOL_CAN_RAW, CAN_RAW_FILTER, NULL, 0);
467468 To set the filters to zero filters is quite obsolete as to not read
469 data causes the raw socket to discard the received CAN frames. But
470 having this 'send only' use-case we may remove the receive list in the
471 Kernel to save a little (really a very little!) CPU usage.
472473 4.1.1.1 CAN filter usage optimisation
474475 The CAN filters are processed in per-device filter lists at CAN frame
476 reception time. To reduce the number of checks that need to be performed
477 while walking through the filter lists the CAN core provides an optimized
478 filter handling when the filter subscription focusses on a single CAN ID.
479480 For the possible 2048 SFF CAN identifiers the identifier is used as an index
481 to access the corresponding subscription list without any further checks.
482 For the 2^29 possible EFF CAN identifiers a 10 bit XOR folding is used as
483 hash function to retrieve the EFF table index.
484485 To benefit from the optimized filters for single CAN identifiers the
486 CAN_SFF_MASK or CAN_EFF_MASK have to be set into can_filter.mask together
487 with set CAN_EFF_FLAG and CAN_RTR_FLAG bits. A set CAN_EFF_FLAG bit in the
488 can_filter.mask makes clear that it matters whether a SFF or EFF CAN ID is
489 subscribed. E.g. in the example from above
490491 rfilter[0].can_id = 0x123;
492 rfilter[0].can_mask = CAN_SFF_MASK;
493494 both SFF frames with CAN ID 0x123 and EFF frames with 0xXXXXX123 can pass.
495496 To filter for only 0x123 (SFF) and 0x12345678 (EFF) CAN identifiers the
497 filter has to be defined in this way to benefit from the optimized filters:
498499 struct can_filter rfilter[2];
500501 rfilter[0].can_id = 0x123;
502 rfilter[0].can_mask = (CAN_EFF_FLAG | CAN_RTR_FLAG | CAN_SFF_MASK);
503 rfilter[1].can_id = 0x12345678 | CAN_EFF_FLAG;
504 rfilter[1].can_mask = (CAN_EFF_FLAG | CAN_RTR_FLAG | CAN_EFF_MASK);
505506 setsockopt(s, SOL_CAN_RAW, CAN_RAW_FILTER, &rfilter, sizeof(rfilter));
507508 4.1.2 RAW socket option CAN_RAW_ERR_FILTER
509510 As described in chapter 3.4 the CAN interface driver can generate so
511 called Error Message Frames that can optionally be passed to the user
512 application in the same way as other CAN frames. The possible
513 errors are divided into different error classes that may be filtered
514 using the appropriate error mask. To register for every possible
515 error condition CAN_ERR_MASK can be used as value for the error mask.
516 The values for the error mask are defined in linux/can/error.h .
517518 can_err_mask_t err_mask = ( CAN_ERR_TX_TIMEOUT | CAN_ERR_BUSOFF );
519520 setsockopt(s, SOL_CAN_RAW, CAN_RAW_ERR_FILTER,
521 &err_mask, sizeof(err_mask));
522523 4.1.3 RAW socket option CAN_RAW_LOOPBACK
524525 To meet multi user needs the local loopback is enabled by default
526 (see chapter 3.2 for details). But in some embedded use-cases
527 (e.g. when only one application uses the CAN bus) this loopback
528 functionality can be disabled (separately for each socket):
529530 int loopback = 0; /* 0 = disabled, 1 = enabled (default) */
531532 setsockopt(s, SOL_CAN_RAW, CAN_RAW_LOOPBACK, &loopback, sizeof(loopback));
533534 4.1.4 RAW socket option CAN_RAW_RECV_OWN_MSGS
535536 When the local loopback is enabled, all the sent CAN frames are
537 looped back to the open CAN sockets that registered for the CAN
538 frames' CAN-ID on this given interface to meet the multi user
539 needs. The reception of the CAN frames on the same socket that was
540 sending the CAN frame is assumed to be unwanted and therefore
541 disabled by default. This default behaviour may be changed on
542 demand:
543544 int recv_own_msgs = 1; /* 0 = disabled (default), 1 = enabled */
545546 setsockopt(s, SOL_CAN_RAW, CAN_RAW_RECV_OWN_MSGS,
547 &recv_own_msgs, sizeof(recv_own_msgs));
548549 4.1.5 RAW socket option CAN_RAW_FD_FRAMES
550551 CAN FD support in CAN_RAW sockets can be enabled with a new socket option
552 CAN_RAW_FD_FRAMES which is off by default. When the new socket option is
553 not supported by the CAN_RAW socket (e.g. on older kernels), switching the
554 CAN_RAW_FD_FRAMES option returns the error -ENOPROTOOPT.
555556 Once CAN_RAW_FD_FRAMES is enabled the application can send both CAN frames
557 and CAN FD frames. OTOH the application has to handle CAN and CAN FD frames
558 when reading from the socket.
559560 CAN_RAW_FD_FRAMES enabled: CAN_MTU and CANFD_MTU are allowed
561 CAN_RAW_FD_FRAMES disabled: only CAN_MTU is allowed (default)
562563 Example:
564 [ remember: CANFD_MTU == sizeof(struct canfd_frame) ]
565566 struct canfd_frame cfd;
567568 nbytes = read(s, &cfd, CANFD_MTU);
569570 if (nbytes == CANFD_MTU) {
571 printf("got CAN FD frame with length %d\n", cfd.len);
572 /* cfd.flags contains valid data */
573 } else if (nbytes == CAN_MTU) {
574 printf("got legacy CAN frame with length %d\n", cfd.len);
575 /* cfd.flags is undefined */
576 } else {
577 fprintf(stderr, "read: invalid CAN(FD) frame\n");
578 return 1;
579 }
580581 /* the content can be handled independently from the received MTU size */
582583 printf("can_id: %X data length: %d data: ", cfd.can_id, cfd.len);
584 for (i = 0; i < cfd.len; i++)
585 printf("%02X ", cfd.data[i]);
586587 When reading with size CANFD_MTU only returns CAN_MTU bytes that have
588 been received from the socket a legacy CAN frame has been read into the
589 provided CAN FD structure. Note that the canfd_frame.flags data field is
590 not specified in the struct can_frame and therefore it is only valid in
591 CANFD_MTU sized CAN FD frames.
592593 Implementation hint for new CAN applications:
594595 To build a CAN FD aware application use struct canfd_frame as basic CAN
596 data structure for CAN_RAW based applications. When the application is
597 executed on an older Linux kernel and switching the CAN_RAW_FD_FRAMES
598 socket option returns an error: No problem. You'll get legacy CAN frames
599 or CAN FD frames and can process them the same way.
600601 When sending to CAN devices make sure that the device is capable to handle
602 CAN FD frames by checking if the device maximum transfer unit is CANFD_MTU.
603 The CAN device MTU can be retrieved e.g. with a SIOCGIFMTU ioctl() syscall.
604605 4.1.6 RAW socket option CAN_RAW_JOIN_FILTERS
606607 The CAN_RAW socket can set multiple CAN identifier specific filters that
608 lead to multiple filters in the af_can.c filter processing. These filters
609 are indenpendent from each other which leads to logical OR'ed filters when
610 applied (see 4.1.1).
611612 This socket option joines the given CAN filters in the way that only CAN
613 frames are passed to user space that matched *all* given CAN filters. The
614 semantic for the applied filters is therefore changed to a logical AND.
615616 This is useful especially when the filterset is a combination of filters
617 where the CAN_INV_FILTER flag is set in order to notch single CAN IDs or
618 CAN ID ranges from the incoming traffic.
619620 4.1.7 RAW socket returned message flags
621622 When using recvmsg() call, the msg->msg_flags may contain following flags:
623624 MSG_DONTROUTE: set when the received frame was created on the local host.
625626 MSG_CONFIRM: set when the frame was sent via the socket it is received on.
627 This flag can be interpreted as a 'transmission confirmation' when the
628 CAN driver supports the echo of frames on driver level, see 3.2 and 6.2.
629 In order to receive such messages, CAN_RAW_RECV_OWN_MSGS must be set.
630631 4.2 Broadcast Manager protocol sockets (SOCK_DGRAM)
632633 The Broadcast Manager protocol provides a command based configuration
634 interface to filter and send (e.g. cyclic) CAN messages in kernel space.
635636 Receive filters can be used to down sample frequent messages; detect events
637 such as message contents changes, packet length changes, and do time-out
638 monitoring of received messages.
639640 Periodic transmission tasks of CAN frames or a sequence of CAN frames can be
641 created and modified at runtime; both the message content and the two
642 possible transmit intervals can be altered.
643644 A BCM socket is not intended for sending individual CAN frames using the
645 struct can_frame as known from the CAN_RAW socket. Instead a special BCM
646 configuration message is defined. The basic BCM configuration message used
647 to communicate with the broadcast manager and the available operations are
648 defined in the linux/can/bcm.h include. The BCM message consists of a
649 message header with a command ('opcode') followed by zero or more CAN frames.
650 The broadcast manager sends responses to user space in the same form:
651652 struct bcm_msg_head {
653 __u32 opcode; /* command */
654 __u32 flags; /* special flags */
655 __u32 count; /* run 'count' times with ival1 */
656 struct timeval ival1, ival2; /* count and subsequent interval */
657 canid_t can_id; /* unique can_id for task */
658 __u32 nframes; /* number of can_frames following */
659 struct can_frame frames[0];
660 };
661662 The aligned payload 'frames' uses the same basic CAN frame structure defined
663 at the beginning of section 4 and in the include/linux/can.h include. All
664 messages to the broadcast manager from user space have this structure.
665666 Note a CAN_BCM socket must be connected instead of bound after socket
667 creation (example without error checking):
668669 int s;
670 struct sockaddr_can addr;
671 struct ifreq ifr;
672673 s = socket(PF_CAN, SOCK_DGRAM, CAN_BCM);
674675 strcpy(ifr.ifr_name, "can0");
676 ioctl(s, SIOCGIFINDEX, &ifr);
677678 addr.can_family = AF_CAN;
679 addr.can_ifindex = ifr.ifr_ifindex;
680681 connect(s, (struct sockaddr *)&addr, sizeof(addr))
682683 (..)
684685 The broadcast manager socket is able to handle any number of in flight
686 transmissions or receive filters concurrently. The different RX/TX jobs are
687 distinguished by the unique can_id in each BCM message. However additional
688 CAN_BCM sockets are recommended to communicate on multiple CAN interfaces.
689 When the broadcast manager socket is bound to 'any' CAN interface (=> the
690 interface index is set to zero) the configured receive filters apply to any
691 CAN interface unless the sendto() syscall is used to overrule the 'any' CAN
692 interface index. When using recvfrom() instead of read() to retrieve BCM
693 socket messages the originating CAN interface is provided in can_ifindex.
694695 4.2.1 Broadcast Manager operations
696697 The opcode defines the operation for the broadcast manager to carry out,
698 or details the broadcast managers response to several events, including
699 user requests.
700701 Transmit Operations (user space to broadcast manager):
702703 TX_SETUP: Create (cyclic) transmission task.
704705 TX_DELETE: Remove (cyclic) transmission task, requires only can_id.
706707 TX_READ: Read properties of (cyclic) transmission task for can_id.
708709 TX_SEND: Send one CAN frame.
710711 Transmit Responses (broadcast manager to user space):
712713 TX_STATUS: Reply to TX_READ request (transmission task configuration).
714715 TX_EXPIRED: Notification when counter finishes sending at initial interval
716 'ival1'. Requires the TX_COUNTEVT flag to be set at TX_SETUP.
717718 Receive Operations (user space to broadcast manager):
719720 RX_SETUP: Create RX content filter subscription.
721722 RX_DELETE: Remove RX content filter subscription, requires only can_id.
723724 RX_READ: Read properties of RX content filter subscription for can_id.
725726 Receive Responses (broadcast manager to user space):
727728 RX_STATUS: Reply to RX_READ request (filter task configuration).
729730 RX_TIMEOUT: Cyclic message is detected to be absent (timer ival1 expired).
731732 RX_CHANGED: BCM message with updated CAN frame (detected content change).
733 Sent on first message received or on receipt of revised CAN messages.
734735 4.2.2 Broadcast Manager message flags
736737 When sending a message to the broadcast manager the 'flags' element may
738 contain the following flag definitions which influence the behaviour:
739740 SETTIMER: Set the values of ival1, ival2 and count
741742 STARTTIMER: Start the timer with the actual values of ival1, ival2
743 and count. Starting the timer leads simultaneously to emit a CAN frame.
744745 TX_COUNTEVT: Create the message TX_EXPIRED when count expires
746747 TX_ANNOUNCE: A change of data by the process is emitted immediately.
748749 TX_CP_CAN_ID: Copies the can_id from the message header to each
750 subsequent frame in frames. This is intended as usage simplification. For
751 TX tasks the unique can_id from the message header may differ from the
752 can_id(s) stored for transmission in the subsequent struct can_frame(s).
753754 RX_FILTER_ID: Filter by can_id alone, no frames required (nframes=0).
755756 RX_CHECK_DLC: A change of the DLC leads to an RX_CHANGED.
757758 RX_NO_AUTOTIMER: Prevent automatically starting the timeout monitor.
759760 RX_ANNOUNCE_RESUME: If passed at RX_SETUP and a receive timeout occurred, a
761 RX_CHANGED message will be generated when the (cyclic) receive restarts.
762763 TX_RESET_MULTI_IDX: Reset the index for the multiple frame transmission.
764765 RX_RTR_FRAME: Send reply for RTR-request (placed in op->frames[0]).
766767 4.2.3 Broadcast Manager transmission timers
768769 Periodic transmission configurations may use up to two interval timers.
770 In this case the BCM sends a number of messages ('count') at an interval
771 'ival1', then continuing to send at another given interval 'ival2'. When
772 only one timer is needed 'count' is set to zero and only 'ival2' is used.
773 When SET_TIMER and START_TIMER flag were set the timers are activated.
774 The timer values can be altered at runtime when only SET_TIMER is set.
775776 4.2.4 Broadcast Manager message sequence transmission
777778 Up to 256 CAN frames can be transmitted in a sequence in the case of a cyclic
779 TX task configuration. The number of CAN frames is provided in the 'nframes'
780 element of the BCM message head. The defined number of CAN frames are added
781 as array to the TX_SETUP BCM configuration message.
782783 /* create a struct to set up a sequence of four CAN frames */
784 struct {
785 struct bcm_msg_head msg_head;
786 struct can_frame frame[4];
787 } mytxmsg;
788789 (..)
790 mytxmsg.nframes = 4;
791 (..)
792793 write(s, &mytxmsg, sizeof(mytxmsg));
794795 With every transmission the index in the array of CAN frames is increased
796 and set to zero at index overflow.
797798 4.2.5 Broadcast Manager receive filter timers
799800 The timer values ival1 or ival2 may be set to non-zero values at RX_SETUP.
801 When the SET_TIMER flag is set the timers are enabled:
802803 ival1: Send RX_TIMEOUT when a received message is not received again within
804 the given time. When START_TIMER is set at RX_SETUP the timeout detection
805 is activated directly - even without a former CAN frame reception.
806807 ival2: Throttle the received message rate down to the value of ival2. This
808 is useful to reduce messages for the application when the signal inside the
809 CAN frame is stateless as state changes within the ival2 periode may get
810 lost.
811812 4.2.6 Broadcast Manager multiplex message receive filter
813814 To filter for content changes in multiplex message sequences an array of more
815 than one CAN frames can be passed in a RX_SETUP configuration message. The
816 data bytes of the first CAN frame contain the mask of relevant bits that
817 have to match in the subsequent CAN frames with the received CAN frame.
818 If one of the subsequent CAN frames is matching the bits in that frame data
819 mark the relevant content to be compared with the previous received content.
820 Up to 257 CAN frames (multiplex filter bit mask CAN frame plus 256 CAN
821 filters) can be added as array to the TX_SETUP BCM configuration message.
822823 /* usually used to clear CAN frame data[] - beware of endian problems! */
824 #define U64_DATA(p) (*(unsigned long long*)(p)->data)
825826 struct {
827 struct bcm_msg_head msg_head;
828 struct can_frame frame[5];
829 } msg;
830831 msg.msg_head.opcode = RX_SETUP;
832 msg.msg_head.can_id = 0x42;
833 msg.msg_head.flags = 0;
834 msg.msg_head.nframes = 5;
835 U64_DATA(&msg.frame[0]) = 0xFF00000000000000ULL; /* MUX mask */
836 U64_DATA(&msg.frame[1]) = 0x01000000000000FFULL; /* data mask (MUX 0x01) */
837 U64_DATA(&msg.frame[2]) = 0x0200FFFF000000FFULL; /* data mask (MUX 0x02) */
838 U64_DATA(&msg.frame[3]) = 0x330000FFFFFF0003ULL; /* data mask (MUX 0x33) */
839 U64_DATA(&msg.frame[4]) = 0x4F07FC0FF0000000ULL; /* data mask (MUX 0x4F) */
840841 write(s, &msg, sizeof(msg));
842843 4.3 connected transport protocols (SOCK_SEQPACKET)
844 4.4 unconnected transport protocols (SOCK_DGRAM)
8458468475. SocketCAN core module
848-------------------------
849850 The SocketCAN core module implements the protocol family
851 PF_CAN. CAN protocol modules are loaded by the core module at
852 runtime. The core module provides an interface for CAN protocol
853 modules to subscribe needed CAN IDs (see chapter 3.1).
854855 5.1 can.ko module params
856857 - stats_timer: To calculate the SocketCAN core statistics
858 (e.g. current/maximum frames per second) this 1 second timer is
859 invoked at can.ko module start time by default. This timer can be
860 disabled by using stattimer=0 on the module commandline.
861862 - debug: (removed since SocketCAN SVN r546)
863864 5.2 procfs content
865866 As described in chapter 3.1 the SocketCAN core uses several filter
867 lists to deliver received CAN frames to CAN protocol modules. These
868 receive lists, their filters and the count of filter matches can be
869 checked in the appropriate receive list. All entries contain the
870 device and a protocol module identifier:
871872 foo@bar:~$ cat /proc/net/can/rcvlist_all
873874 receive list 'rx_all':
875 (vcan3: no entry)
876 (vcan2: no entry)
877 (vcan1: no entry)
878 device can_id can_mask function userdata matches ident
879 vcan0 000 00000000 f88e6370 f6c6f400 0 raw
880 (any: no entry)
881882 In this example an application requests any CAN traffic from vcan0.
883884 rcvlist_all - list for unfiltered entries (no filter operations)
885 rcvlist_eff - list for single extended frame (EFF) entries
886 rcvlist_err - list for error message frames masks
887 rcvlist_fil - list for mask/value filters
888 rcvlist_inv - list for mask/value filters (inverse semantic)
889 rcvlist_sff - list for single standard frame (SFF) entries
890891 Additional procfs files in /proc/net/can
892893 stats - SocketCAN core statistics (rx/tx frames, match ratios, ...)
894 reset_stats - manual statistic reset
895 version - prints the SocketCAN core version and the ABI version
896897 5.3 writing own CAN protocol modules
898899 To implement a new protocol in the protocol family PF_CAN a new
900 protocol has to be defined in include/linux/can.h .
901 The prototypes and definitions to use the SocketCAN core can be
902 accessed by including include/linux/can/core.h .
903 In addition to functions that register the CAN protocol and the
904 CAN device notifier chain there are functions to subscribe CAN
905 frames received by CAN interfaces and to send CAN frames:
906907 can_rx_register - subscribe CAN frames from a specific interface
908 can_rx_unregister - unsubscribe CAN frames from a specific interface
909 can_send - transmit a CAN frame (optional with local loopback)
910911 For details see the kerneldoc documentation in net/can/af_can.c or
912 the source code of net/can/raw.c or net/can/bcm.c .
9139146. CAN network drivers
915----------------------
916917 Writing a CAN network device driver is much easier than writing a
918 CAN character device driver. Similar to other known network device
919 drivers you mainly have to deal with:
920921 - TX: Put the CAN frame from the socket buffer to the CAN controller.
922 - RX: Put the CAN frame from the CAN controller to the socket buffer.
923924 See e.g. at Documentation/networking/netdevices.txt . The differences
925 for writing CAN network device driver are described below:
926927 6.1 general settings
928929 dev->type = ARPHRD_CAN; /* the netdevice hardware type */
930 dev->flags = IFF_NOARP; /* CAN has no arp */
931932 dev->mtu = CAN_MTU; /* sizeof(struct can_frame) -> legacy CAN interface */
933934 or alternative, when the controller supports CAN with flexible data rate:
935 dev->mtu = CANFD_MTU; /* sizeof(struct canfd_frame) -> CAN FD interface */
936937 The struct can_frame or struct canfd_frame is the payload of each socket
938 buffer (skbuff) in the protocol family PF_CAN.
939940 6.2 local loopback of sent frames
941942 As described in chapter 3.2 the CAN network device driver should
943 support a local loopback functionality similar to the local echo
944 e.g. of tty devices. In this case the driver flag IFF_ECHO has to be
945 set to prevent the PF_CAN core from locally echoing sent frames
946 (aka loopback) as fallback solution:
947948 dev->flags = (IFF_NOARP | IFF_ECHO);
949950 6.3 CAN controller hardware filters
951952 To reduce the interrupt load on deep embedded systems some CAN
953 controllers support the filtering of CAN IDs or ranges of CAN IDs.
954 These hardware filter capabilities vary from controller to
955 controller and have to be identified as not feasible in a multi-user
956 networking approach. The use of the very controller specific
957 hardware filters could make sense in a very dedicated use-case, as a
958 filter on driver level would affect all users in the multi-user
959 system. The high efficient filter sets inside the PF_CAN core allow
960 to set different multiple filters for each socket separately.
961 Therefore the use of hardware filters goes to the category 'handmade
962 tuning on deep embedded systems'. The author is running a MPC603e
963 @133MHz with four SJA1000 CAN controllers from 2002 under heavy bus
964 load without any problems ...
965966 6.4 The virtual CAN driver (vcan)
967968 Similar to the network loopback devices, vcan offers a virtual local
969 CAN interface. A full qualified address on CAN consists of
970971 - a unique CAN Identifier (CAN ID)
972 - the CAN bus this CAN ID is transmitted on (e.g. can0)
973974 so in common use cases more than one virtual CAN interface is needed.
975976 The virtual CAN interfaces allow the transmission and reception of CAN
977 frames without real CAN controller hardware. Virtual CAN network
978 devices are usually named 'vcanX', like vcan0 vcan1 vcan2 ...
979 When compiled as a module the virtual CAN driver module is called vcan.ko
980981 Since Linux Kernel version 2.6.24 the vcan driver supports the Kernel
982 netlink interface to create vcan network devices. The creation and
983 removal of vcan network devices can be managed with the ip(8) tool:
984985 - Create a virtual CAN network interface:
986 $ ip link add type vcan
987988 - Create a virtual CAN network interface with a specific name 'vcan42':
989 $ ip link add dev vcan42 type vcan
990991 - Remove a (virtual CAN) network interface 'vcan42':
992 $ ip link del vcan42
993994 6.5 The CAN network device driver interface
995996 The CAN network device driver interface provides a generic interface
997 to setup, configure and monitor CAN network devices. The user can then
998 configure the CAN device, like setting the bit-timing parameters, via
999 the netlink interface using the program "ip" from the "IPROUTE2"
1000 utility suite. The following chapter describes briefly how to use it.
1001 Furthermore, the interface uses a common data structure and exports a
1002 set of common functions, which all real CAN network device drivers
1003 should use. Please have a look to the SJA1000 or MSCAN driver to
1004 understand how to use them. The name of the module is can-dev.ko.
10051006 6.5.1 Netlink interface to set/get devices properties
10071008 The CAN device must be configured via netlink interface. The supported
1009 netlink message types are defined and briefly described in
1010 "include/linux/can/netlink.h". CAN link support for the program "ip"
1011 of the IPROUTE2 utility suite is available and it can be used as shown
1012 below:
10131014 - Setting CAN device properties:
10151016 $ ip link set can0 type can help
1017 Usage: ip link set DEVICE type can
1018 [ bitrate BITRATE [ sample-point SAMPLE-POINT] ] |
1019 [ tq TQ prop-seg PROP_SEG phase-seg1 PHASE-SEG1
1020 phase-seg2 PHASE-SEG2 [ sjw SJW ] ]
10211022 [ loopback { on | off } ]
1023 [ listen-only { on | off } ]
1024 [ triple-sampling { on | off } ]
10251026 [ restart-ms TIME-MS ]
1027 [ restart ]
10281029 Where: BITRATE := { 1..1000000 }
1030 SAMPLE-POINT := { 0.000..0.999 }
1031 TQ := { NUMBER }
1032 PROP-SEG := { 1..8 }
1033 PHASE-SEG1 := { 1..8 }
1034 PHASE-SEG2 := { 1..8 }
1035 SJW := { 1..4 }
1036 RESTART-MS := { 0 | NUMBER }
10371038 - Display CAN device details and statistics:
10391040 $ ip -details -statistics link show can0
1041 2: can0: <NOARP,UP,LOWER_UP,ECHO> mtu 16 qdisc pfifo_fast state UP qlen 10
1042 link/can
1043 can <TRIPLE-SAMPLING> state ERROR-ACTIVE restart-ms 100
1044 bitrate 125000 sample_point 0.875
1045 tq 125 prop-seg 6 phase-seg1 7 phase-seg2 2 sjw 1
1046 sja1000: tseg1 1..16 tseg2 1..8 sjw 1..4 brp 1..64 brp-inc 1
1047 clock 8000000
1048 re-started bus-errors arbit-lost error-warn error-pass bus-off
1049 41 17457 0 41 42 41
1050 RX: bytes packets errors dropped overrun mcast
1051 140859 17608 17457 0 0 0
1052 TX: bytes packets errors dropped carrier collsns
1053 861 112 0 41 0 0
10541055 More info to the above output:
10561057 "<TRIPLE-SAMPLING>"
1058 Shows the list of selected CAN controller modes: LOOPBACK,
1059 LISTEN-ONLY, or TRIPLE-SAMPLING.
10601061 "state ERROR-ACTIVE"
1062 The current state of the CAN controller: "ERROR-ACTIVE",
1063 "ERROR-WARNING", "ERROR-PASSIVE", "BUS-OFF" or "STOPPED"
10641065 "restart-ms 100"
1066 Automatic restart delay time. If set to a non-zero value, a
1067 restart of the CAN controller will be triggered automatically
1068 in case of a bus-off condition after the specified delay time
1069 in milliseconds. By default it's off.
10701071 "bitrate 125000 sample-point 0.875"
1072 Shows the real bit-rate in bits/sec and the sample-point in the
1073 range 0.000..0.999. If the calculation of bit-timing parameters
1074 is enabled in the kernel (CONFIG_CAN_CALC_BITTIMING=y), the
1075 bit-timing can be defined by setting the "bitrate" argument.
1076 Optionally the "sample-point" can be specified. By default it's
1077 0.000 assuming CIA-recommended sample-points.
10781079 "tq 125 prop-seg 6 phase-seg1 7 phase-seg2 2 sjw 1"
1080 Shows the time quanta in ns, propagation segment, phase buffer
1081 segment 1 and 2 and the synchronisation jump width in units of
1082 tq. They allow to define the CAN bit-timing in a hardware
1083 independent format as proposed by the Bosch CAN 2.0 spec (see
1084 chapter 8 of http://www.semiconductors.bosch.de/pdf/can2spec.pdf).
10851086 "sja1000: tseg1 1..16 tseg2 1..8 sjw 1..4 brp 1..64 brp-inc 1
1087 clock 8000000"
1088 Shows the bit-timing constants of the CAN controller, here the
1089 "sja1000". The minimum and maximum values of the time segment 1
1090 and 2, the synchronisation jump width in units of tq, the
1091 bitrate pre-scaler and the CAN system clock frequency in Hz.
1092 These constants could be used for user-defined (non-standard)
1093 bit-timing calculation algorithms in user-space.
10941095 "re-started bus-errors arbit-lost error-warn error-pass bus-off"
1096 Shows the number of restarts, bus and arbitration lost errors,
1097 and the state changes to the error-warning, error-passive and
1098 bus-off state. RX overrun errors are listed in the "overrun"
1099 field of the standard network statistics.
11001101 6.5.2 Setting the CAN bit-timing
11021103 The CAN bit-timing parameters can always be defined in a hardware
1104 independent format as proposed in the Bosch CAN 2.0 specification
1105 specifying the arguments "tq", "prop_seg", "phase_seg1", "phase_seg2"
1106 and "sjw":
11071108 $ ip link set canX type can tq 125 prop-seg 6 \
1109 phase-seg1 7 phase-seg2 2 sjw 1
11101111 If the kernel option CONFIG_CAN_CALC_BITTIMING is enabled, CIA
1112 recommended CAN bit-timing parameters will be calculated if the bit-
1113 rate is specified with the argument "bitrate":
11141115 $ ip link set canX type can bitrate 125000
11161117 Note that this works fine for the most common CAN controllers with
1118 standard bit-rates but may *fail* for exotic bit-rates or CAN system
1119 clock frequencies. Disabling CONFIG_CAN_CALC_BITTIMING saves some
1120 space and allows user-space tools to solely determine and set the
1121 bit-timing parameters. The CAN controller specific bit-timing
1122 constants can be used for that purpose. They are listed by the
1123 following command:
11241125 $ ip -details link show can0
1126 ...
1127 sja1000: clock 8000000 tseg1 1..16 tseg2 1..8 sjw 1..4 brp 1..64 brp-inc 1
11281129 6.5.3 Starting and stopping the CAN network device
11301131 A CAN network device is started or stopped as usual with the command
1132 "ifconfig canX up/down" or "ip link set canX up/down". Be aware that
1133 you *must* define proper bit-timing parameters for real CAN devices
1134 before you can start it to avoid error-prone default settings:
11351136 $ ip link set canX up type can bitrate 125000
11371138 A device may enter the "bus-off" state if too many errors occurred on
1139 the CAN bus. Then no more messages are received or sent. An automatic
1140 bus-off recovery can be enabled by setting the "restart-ms" to a
1141 non-zero value, e.g.:
11421143 $ ip link set canX type can restart-ms 100
11441145 Alternatively, the application may realize the "bus-off" condition
1146 by monitoring CAN error message frames and do a restart when
1147 appropriate with the command:
11481149 $ ip link set canX type can restart
11501151 Note that a restart will also create a CAN error message frame (see
1152 also chapter 3.4).
11531154 6.6 CAN FD (flexible data rate) driver support
11551156 CAN FD capable CAN controllers support two different bitrates for the
1157 arbitration phase and the payload phase of the CAN FD frame. Therefore a
1158 second bit timing has to be specified in order to enable the CAN FD bitrate.
11591160 Additionally CAN FD capable CAN controllers support up to 64 bytes of
1161 payload. The representation of this length in can_frame.can_dlc and
1162 canfd_frame.len for userspace applications and inside the Linux network
1163 layer is a plain value from 0 .. 64 instead of the CAN 'data length code'.
1164 The data length code was a 1:1 mapping to the payload length in the legacy
1165 CAN frames anyway. The payload length to the bus-relevant DLC mapping is
1166 only performed inside the CAN drivers, preferably with the helper
1167 functions can_dlc2len() and can_len2dlc().
11681169 The CAN netdevice driver capabilities can be distinguished by the network
1170 devices maximum transfer unit (MTU):
11711172 MTU = 16 (CAN_MTU) => sizeof(struct can_frame) => 'legacy' CAN device
1173 MTU = 72 (CANFD_MTU) => sizeof(struct canfd_frame) => CAN FD capable device
11741175 The CAN device MTU can be retrieved e.g. with a SIOCGIFMTU ioctl() syscall.
1176 N.B. CAN FD capable devices can also handle and send legacy CAN frames.
11771178 FIXME: Add details about the CAN FD controller configuration when available.
11791180 6.7 Supported CAN hardware
11811182 Please check the "Kconfig" file in "drivers/net/can" to get an actual
1183 list of the support CAN hardware. On the SocketCAN project website
1184 (see chapter 7) there might be further drivers available, also for
1185 older kernel versions.
118611877. SocketCAN resources
1188-----------------------
11891190 The Linux CAN / SocketCAN project ressources (project site / mailing list)
1191 are referenced in the MAINTAINERS file in the Linux source tree.
1192 Search for CAN NETWORK [LAYERS|DRIVERS].
119311948. Credits
1195----------
11961197 Oliver Hartkopp (PF_CAN core, filters, drivers, bcm, SJA1000 driver)
1198 Urs Thuermann (PF_CAN core, kernel integration, socket interfaces, raw, vcan)
1199 Jan Kizka (RT-SocketCAN core, Socket-API reconciliation)
1200 Wolfgang Grandegger (RT-SocketCAN core & drivers, Raw Socket-API reviews,
1201 CAN device driver interface, MSCAN driver)
1202 Robert Schwebel (design reviews, PTXdist integration)
1203 Marc Kleine-Budde (design reviews, Kernel 2.6 cleanups, drivers)
1204 Benedikt Spranger (reviews)
1205 Thomas Gleixner (LKML reviews, coding style, posting hints)
1206 Andrey Volkov (kernel subtree structure, ioctls, MSCAN driver)
1207 Matthias Brukner (first SJA1000 CAN netdevice implementation Q2/2003)
1208 Klaus Hitschler (PEAK driver integration)
1209 Uwe Koppe (CAN netdevices with PF_PACKET approach)
1210 Michael Schulze (driver layer loopback requirement, RT CAN drivers review)
1211 Pavel Pisa (Bit-timing calculation)
1212 Sascha Hauer (SJA1000 platform driver)
1213 Sebastian Haas (SJA1000 EMS PCI driver)
1214 Markus Plessing (SJA1000 EMS PCI driver)
1215 Per Dalen (SJA1000 Kvaser PCI driver)
1216 Sam Ravnborg (reviews, coding style, kbuild help)